I've heard that accessing let and const values before they are initialized can cause a ReferenceError because of something called the temporal dead zone.  What is the temporal dead zone, how does it relate to scope and hoisting, and in what sit...
I've recently come across the const keyword in JavaScript. From what I can tell, it is used to create immutable variables, and I've tested to ensure that it cannot be redefined (in Node.js):  const x = 'const'; const x = 'not-co...
There's the const definition in Exploring ES6 by Dr. Axel Rauschmayer:     const works like let, but the variable you declare must be   immediately initialized, with a value that can’t be changed   afterwards. […]  const bar = 123; bar = 45...
Regardless of functional differences, does using the new keywords 'let' and 'const' have any generalized or specific impact on performance relative to 'var'?  After running the program:  function timeit(f, N, S) {     var star...
I always thought that const variables in JavaScript would be constants... like "variables that cannot change". So I always assumed the benefit of using const over let/var would be something like decreased resources usage. But after a quick te...
When I try to define a variable using var, everything is working.  But defining it as const is not working as expected and the variable is undefined.    window.eval("var v = 5;"); document.body.innerHTML += window.v === undefined;  window.eva...
Constants are block-scoped, much like variables defined using the let statement. The value of a constant cannot change through re-assignment, and it can't be redeclared.   As per MDN The value of a constant cannot change through re-assignment,...
I would like to declare a type-enforced array of items and be able to derive a union type from it. This pattern works if you do not explicitly give a type to the items in the array. I am not sure how to best explain it so here is an example:  EXAMPLE...
In the process of learning JavaScript I learned that Let and const were introduced to fix the problems of Var regarding the global scope and hoisting and not giving an error if re-declared.  Now can I write the code completely without using var ? or...
Hi I am new to react so sorry for the basic question.  I am trying to define a method in a const   const Age = t.refinement(t.Number, (n) => return n >= 18);   However, the linter doesn't like that i have a return keyword in the method. Her...

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